The breathing pattern and ventilatory response to carbon dioxide of 10 experienced divers was compared with that of 10 nondivers of similar age and build. Breathing pattern was described by the equation VE = M (VT - K) and the response to carbon dioxide by VE = S(PCO2 - B). The divers exhibited a value form 27% lower than the nondivers; S was 33% lower. The difference was significant (P less than 0.05) in both cases. B was significantly higher (P less than 0.05) in the divers than nondivers. These differences are not attributable to age, build, or vital capacity. S was well correlated with M when all subjects were considered a single group. Within the diving group no correlation of S and M with diving experience was found.